after it first starts raining the water soaks the payment and fills in all the cracks and crevices the oil floats on water so now you have a film of oil on top of a cushion of water and since water is self leveling a very smooth surface the oil soon washes away oh and by the way areas around stop lights are the worst cars waiting for the light drip oil grease tranny fulid antifreeze etc and this is where you need the road friction to stop